[](https://nodei.co/npm/acorn-es7-plugin/)
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acorn-es7-plugin
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======
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acorn-es7-plugin is a plugin for the [Acorn](https://github.com/marijnh/acorn) parser that generates ESTrees following the ['experimental' specification](https://github.com/estree/estree/blob/master/experimental/async-functions.md) for asynchronous functions.
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npm install --save acorn-es7-plugin
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Usage
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=====
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Adding the plugin
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// Require acorn as usual
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var acorn = require("acorn");
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// Add the es7-plugin
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require('./acorn-es7-plugin')(acorn) ;
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Using the plugin
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var code = "async function x(){ if (x) return await(x-1) ; return 0 ; }\n";
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var ast = acorn.parse(code,{
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// Specify use of the plugin
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plugins:{asyncawait:true},
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// Specify the ecmaVersion
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ecmaVersion:7
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}) ;
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// Show the AST
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console.log(JSON.stringify(ast,null,2)) ;
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Output:
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{
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"type": "Program",
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"body": [
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{
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"type": "FunctionDeclaration",
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"id": {
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"type": "Identifier",
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"name": "x"
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},
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"generator": false,
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"expression": false,
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"params": [],
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"body": {
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"type": "BlockStatement",
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"body": [
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{
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"type": "IfStatement",
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"test": {
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"type": "Identifier",
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"name": "x"
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},
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"consequent": {
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"type": "ReturnStatement",
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"argument": {
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"type": "AwaitExpression",
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"operator": "await",
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"argument": {
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"type": "BinaryExpression",
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"left": {
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"type": "Identifier",
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"name": "x"
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},
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"operator": "-",
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"right": {
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"type": "Literal",
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"value": 1,
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"raw": "1"
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}
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}
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}
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},
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"alternate": null
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},
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{
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"type": "ReturnStatement",
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"argument": {
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"type": "Literal",
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"value": 0,
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"raw": "0"
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}
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}
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]
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},
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"async": true
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}
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],
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"sourceType": "script"
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}
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Options & Compliance
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====================
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The parser attempts to enforce strict contextualisation of `async` and `await`. Specifically, `async` is only a keyword if it precedes a function declaration, function expression or arrow function. `await` is only a keyword inside an `async` function. Outside of these contexts, both tokens are treated as identifiers (as they were in ES6 and earlier).
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When using the plugin, you can supply an object in place of the 'true' flag with the following options.
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| flag | meaning |
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|------|---------|
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| awaitAnywhere | If `await` is used outside of an async function and could not be an identifier, generate an AwaitExpression node. This typically means you can use `await` anywhere _except_ when its argument would require parentheses, as this parses to a call to 'await(....)'. Should not be used with inAsyncFunction option |
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| inAsyncFunction | Parse the code as if it is the body of an `async function`. This means `await` cannot be an identifier and is always an AwaitExpression, even if the argument is parenthesized. Should not be used with the awaitAnywhere option |
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| asyncExits | Allow the additional sequences `async return <optional-expression>` and `async throw <expression>`. These sequences are used with [nodent](https://github.com/MatAtBread/nodent). In each case, as with async functions, a standard ReturnStatement (or ThrowStatement) node is generated, with an additional member 'async' set to true.
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The parser also accepts async getters in object literals and classes, which is currently disallowed by the ES7 specification.
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Changelog
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=========
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30-Mar-17: v1.1.7
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- Fix parsing of IIAFE `(async function (){ }())` with acorn v3.
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07-Oct-16: v1.1.1
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- Fix disambiguation of async, get and set tokens (and add tests) when defining object properties:
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| Code | Interpretation
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|-----------------------|-------------------------|
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| `get async(){}` | Is a standard ES6 getter called 'async'
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| `set async(v){}` | Is a standard ES6 setter called 'async'
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| `async get(...){}` | Is a standard ES7 async method called 'get'
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| `async set(...){}` | Is a standard ES7 async method called 'set'
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| `async get x(){}` | Is an extension that defines an async getter called 'x'
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| `get async x(){}` | Is an extension that defines an async getter called 'x', but is deprecated (`async` should proceed `get`)
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In previous version of the plugin, the standard ES7 constructs were hidden by the plugin extensions and a SyntaxError was incorrectly thrown
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25-Sep-16: v1.1.0
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- Update to work with acorn v4 if present. Note that `async` and `await` are fully parsed by acorn v4. The only use case for the plugin with acorn v4 is with the flags above which are enable specific parsing modes.
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24-Sep-16: v1.0.18
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- Correctly parse `async(()=>0)` as a call to the Identifer 'async', not a failed attempt to define an async arrow.
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20-Jul-16: v1.0.17
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- Correctly set non-standard "range" property on async nodes, as used by Webpack
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27-Jun-16: v1.0.15
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- Fix issue parsing async methods in classes and object literals which (incorrectly) required the `awaitAnywhere` option ([see https://github.com/MatAtBread/acorn-es7-plugin/issues/12](https://github.com/MatAtBread/acorn-es7-plugin/issues/12))
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03-May-16: v1.0.14
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- Correctly parse async statements containing comments.
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- Implement the option inAsyncFunction
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03-May-16: v1.0.13
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- Correctly parse the statement `export async function name(){...}` as _async function name(){...}_ is a valid named declaration.
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26-Feb-16: v1.0.12
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- Updated to return the original acorn object on installation. See https://github.com/MatAtBread/acorn-es7-plugin/pull/4
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19-Dec-15: v1.0.11
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- Generate error if 'await' is used as an identifier within an async function.
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10-Dec-15: v1.0.10
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- Update the plugin code to remove 'async' and 'await' from the super-strict keyword tests introduced in acorn v2.6.x that generate parse errors before the plugin gets a chance to manage them.
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